1. Technical Field
An aspect of the present disclosure relates to an electrophoretic display sheet, an electrophoretic display device, and an electronic apparatus using electrophoretic migration in which charged particles in a medium migrate by applying a voltage to form images, in particular, an electrophoretic display device, and an electronic apparatus enabling to avoid damage to a driving circuit by reducing stress applied to a driving substrate when an electrophoretic display sheet is attached to the driving substrate.
2. Related Art
An electrophoretic display device (so-called EPD display device) provided with an electrophoretic element is a display device using electrophoretic migration in which particles dispersed in a solvent migrate by applying a voltage. As for methods for electrophoretic migration, for example, a microcapsule type, a horizontal migration type, and a vertical type have been developed. EPD display devices are easily processed and handled compared to LCDs, thereby being expected to be used for mobile equipment and information equipment.
An electrophoretic display device is formed by attaching an electrophoretic display sheet in which an electrophoretic element is formed on a transparent plastic substrate, and a driving substrate provided with an element and an electrode driving the electrophoretic display sheet.
Stress caused in an attaching process makes an end of an electrophoretic display sheet dig into a driving substrate, and a transparent electrode provided on an electrophoretic display sheet comes in contact with a driving electrode, causing a short circuit or damage to a circuit of a thin-film transistor. To avoid such problems, a protection sheet is commonly formed on an end of a driving substrate to protect a driving circuit from an end of an electrophoretic display sheet.
However, in a method of related art, a process to attach a protection sheet is required. In addition, a space having a certain area is needed to attach the protection sheet on a driving substrate.
Further, a protection sheet normally needs to have the thickness from about 50 μm to 100 μm to ensure strength as a sheet. This thickness is larger than that of a display layer of an electrophoretic capsule (from 20 μm to 30 μm, for example), resulting in problems such as uplift of an electrophoretic display sheet around the protection sheet, and degradation of an electric characteristic.
When a soft material such as a plastic substrate is used as a rear substrate provided on a driving substrate to make an electrophoretic display flexible, aforementioned problems become even more prominent. That is, a driving circuit is susceptible to stress because of being formed on a plastic substrate. Therefore, a driving circuit on a plastic substrate is easily damaged by stress concentration when a driving substrate is pressed with an end of an electrophoretic display sheet to attach thereto.
The aforementioned problem may be avoided by designing an end of a transparent substrate to be formed outside of a circuit region of a driving substrate if an end of the driving substrate is not provided with an external connection terminal. However, in this case, unwanted patterns such as wiring and a driving circuit are displayed on the electrophoretic display sheet.
Further, if an end of a driving substrate is provided with an external connection terminal, unwanted patterns such as for wiring and a driving circuit are also displayed on an electrophoretic display sheet because of wiring communicating a circuit region on the driving substrate with the external connection terminal.